Mysterium Fidei, a Latin phrase meaning mystery of faith or mystery of the faith, is a Christian theological term for an article of faith or doctrine which defies man’s ability to grasp fully. Examples such as the Trinity are mentioned in the Catechism of the Catholic Church, 1066-1068.
Phrase in Mass of the Roman Rite
The phrase mysterium fidei appears in the Roman RiteCanon of the Mass without a clear indication of what mystery it refers to.
In the Tridentine form of the Canon, it was inserted, within the Words of Institution, into the formula of consecration of the wine, as follows:[1]
Text (in Latin)
Simili modo postquam cenatum est,
accipiens et hunc praeclarum calicem
in sanctas ac venerabiles manus suas:
item tibi gratias agens, benedixit,
deditque discipulis suis, dicens:
Accipite, et bibite ex eo omnes.
Hic est enim calix sanguinis mei,
novi et aeterni testamenti:
mysterium fidei:
qui pro vobis et pro multis effundetur
in remissionem peccatorum.
Haec quotiescumque feceritis,
in mei memoriam facietis.
English translation (1959 Daily Missal of the Mystical Body)
In like manner, when he had eaten,
taking also the blessed cup into his
holy and venerable hands, and
again giving thanks to You, He blessed it,
and gave it to His disciples, saying:
Take and drink you all of this:
For this is the Chalice of my blood,
of the new and everlasting covenant:
the mystery of faith:
which shall be shed for you and for many
others unto the remission of sins.
As often as you shall do these things,
you shall do them in memory of me.
In the Tridentine Mass the people do not hear the phrase "mysterium fidei", because the priest speaks the words of the Canon of the Mass inaudibly.
Since the revision of the Roman Missal that was promulgated officially in 1969 and was actually published in 1970, the words "mysterium fidei" have been moved to immediately after the consecration, the showing of the chalice to the congregation and the priest's genuflection. The priest celebrating the Mass proclaims the words, and the people respond with one of the Memorial Acclamations. The same position is assigned to the phrase also in the newer Eucharistic Prayers of the Roman Rite.
Thus, the corresponding text in the Roman Canon or First Eucharistic Prayer is now as follows[2] (here accompanied by the 1973 ICEL translation, due to be replaced soon with a more literal translation):